From owner-freebsd-net@FreeBSD.ORG Tue Mar 16 15:54:16 2004 Return-Path: Delivered-To: freebsd-net@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 6E34216A4CE; Tue, 16 Mar 2004 15:54:16 -0800 (PST) Received: from tigra.ip.net.ua (tigra.ip.net.ua [82.193.96.10]) by mx1.FreeBSD.org (Postfix) with ESMTP id A0FAD43D31; Tue, 16 Mar 2004 15:54:15 -0800 (PST) (envelope-from ru@ip.net.ua) Received: from heffalump.ip.net.ua (heffalump.ip.net.ua [82.193.96.213]) by tigra.ip.net.ua (8.12.10/8.12.9) with ESMTP id i2GNwbee051379 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Wed, 17 Mar 2004 01:58:39 +0200 (EET) (envelope-from ru@ip.net.ua) Received: (from ru@localhost) by heffalump.ip.net.ua (8.12.11/8.12.11) id i2GNsHiM048275; Wed, 17 Mar 2004 01:54:17 +0200 (EET) (envelope-from ru) Date: Wed, 17 Mar 2004 01:54:17 +0200 From: Ruslan Ermilov To: Dag-Erling Sm?rgrav Message-ID: <20040316235417.GC65466@ip.net.ua> References: <20040316225230.GO3462@ip.net.ua> <20040316232848.GR3462@ip.net.ua> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="zCKi3GIZzVBPywwA" Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.6i X-Spam-Checker-Version: SpamAssassin 2.55 (1.174.2.19-2003-05-19-exp) cc: current@freebsd.org cc: net@freebsd.org Subject: Re: libalias patch for review / testing X-BeenThere: freebsd-net@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: Networking and TCP/IP with FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 16 Mar 2004 23:54:16 -0000 --zCKi3GIZzVBPywwA Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Wed, Mar 17, 2004 at 12:34:46AM +0100, Dag-Erling Sm?rgrav wrote: > Ruslan Ermilov writes: > > : `-fstrict-aliasing' > > : Allows the compiler to assume the strictest aliasing rules > > : applicable to the language being compiled. For C (and C++), this > > : activates optimizations based on the type of expressions. In > > : particular, an object of one type is assumed never to reside at > > : the same address as an object of a different type, unless the > > : types are almost the same. For example, an `unsigned int' can > > : alias an `int', but not a `void*' or a `double'. A character ty= pe > > : may alias any other type. > > > > And asking myself a question: should those (void *)'s in your patch > > be (char *)'s instead, e.g., in twowords() and DifferentialChecksum(), > > or am I misreading the above? >=20 > You're misreading, we're doing u_short * <-> void * (both pointers) > but the man page speaks about int <-> void * (scalar vs pointer) >=20 OK, I stand corrected. ;) > Also, I doubt DifferentialChecksum() is a problem, since it's a > function call. I think the problem may be in the code I've replaced > with calls to twowords(). >=20 Hmm, now that I think about it more, since -O2 turns -fstrict-aliasing, and the latter may produce broken code if strict aliasing rules are broken by the source, I think people (and tinderboxes!) should compile with ``-O2 -Wstrict-aliasing'' in CFLAGS rather than just -O2. For WARNS > 1 compiled code, this will be a no-op (as -Wall implies -Wstrict-aliasing), but it should help catch bugs related to breaking strict aliasing like in libalias, in code that is otherwise compiled without warnings. Cheers, --=20 Ruslan Ermilov FreeBSD committer ru@FreeBSD.org --zCKi3GIZzVBPywwA Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.4 (FreeBSD) iD8DBQFAV5OpUkv4P6juNwoRAkGQAJ4sQy7mMiNCgX4b7vsc2HS+ZKYbHgCfcApJ Sbn6Z6pnxETzw2ZoQphZWXk= =tR29 -----END PGP SIGNATURE----- --zCKi3GIZzVBPywwA--